The tumor we are using in this research project is the Sarcoma I (Sa I) which is maintained in the ascites form in syngeneic A/J (H-2a) mice by weekly serial transplantation, and in the form of a tissue culture cell line. Injection of 10 to the 3rd power-10 to the 4th power Sa I tumor cells kills 60-80% of A/J mice in 30-50 days. Immunity to this challenge dose can be induced in A/J mice by pretreatment with irradiated Sa I tumor cells. Enhancement of Sa I tumor growth occurs when A/J miie are pre-treated with 10-12 day old syngeneic fetal cells. Using this tumor-host system, we demonstrated that cross-reacting antigens exist on fetal, sperm, and tumor cells. The specific aims of this research project are: (1) To identify and to characterize these cross-reacting antigens; (2) To study the immunological consequences of immunity against the Sa I tumor on fetal and sperm development in A/J mice; and (3) To extend these studies to other tumor-host systems. These studies should enable a more comprehensive understanding of the immunochemical nature of tumor-associated antigens and of the consequences of immune reactions against these antigens.